The context of this proposal is that of biological energy transductions, which provide the basis for living cell activity. The spinach chloroplast system is a well defined one which can accomplish the conversions between light, oxidative electron transport, hydrogen ion translocation to create either a pH gradient or a membrane potential, and ATP synthesis. It offers the further advantage that the reversible ATPases, or coupling factor protein can be detached easily, then assayed for enzyme activity and used to re-couple depleted membranes. Previous work has demonstrated that the coupling factor undergoes conformational changes caused by energetic stress on the membrane to which it is bound, and our working hypothesis is that these movements may be needed for, or even represent part of the direct driving force for ATP synthesis. The broad objectives are to help define the significant regions of the coupling factor. These regions (with probable degrees of overlap) include: (a) the active site(s) for ATP hydrolysis and for ATP synthesis; (b) the region of interaction with the membrane; and (c) those parts that are hidden from solvent water ordinarily but are exposed during the energy-dependent conformational change. Covalent chemical modification will be the primary tool used. Chemicals with some specificity for particular amino acid side chains will be examined for their inhibition of ATPase or ATP synthesis, with respect to (a); that bind only to detached coupling factor for an initial estimate of (b); and whose attachment (with or without inhibition of activity) is energy-dependent for (c). A better understanding of the significance of any chemical modification will be sought by generating structural data for the subunit polypeptides of this enzyme. These will be separated in moderately large amounts, amino acid composition re-examined, -SH and disulfide bridges located as a function of prior treatment of the chloroplasts, peptide maps established, and to the extent that collaboration is possible, some sequence work initiated.